1. Field of the Invention
The present invention relates generally to a semiconductor device with a titanium film and a fabrication process thereof. More specifically, the invention relates to an improvement in and relating to a process of forming a barrier metal using a chemical vapor deposition.
2. Description of the Related Art
Down-sizing and increasing of package density of semiconductor device has still been furiously progressed. At the present, a prototype of ultra-highly integrated semiconductor devices, such as memory devices, logic devices or so forth, designed according to a dimensional standard of about 0.15 xcexcm, have been fabricated. A diameter of a contact hole associating with increasing of package density of such semiconductor device is further reduced. On the other hand, a depth of the contact hole is difficult to reduce for requirement of a wiring resistance or capacity. Therefore, in the recent years, an aspect ratio of the contact hole is abruptly increasing. Associating therewith, a barrier metal layer is normally provided at least in a bottom portion of the contact hole. The barrier metal layer has a function to prevent mutual dispersion of silicon into a metal forming a metal wiring and a diffusion layer of silicon and to prevent increasing of a contact resistance.
As a method of fabricating the barrier metal in the contact hole, attention has been recently attracted to a chemical vapor deposition method. Hereinafter, as one example of a conventional method, discussion will be given with reference to FIG. 1. At first, as shown in FIG. 1(A), an isolative oxide layer 2 in a thickness of 200 nm is formed on a silicon substrate 1, and a predetermined impurity is implanted into the silicon substrate 1 to form a diffusion layer 3. Subsequently, an insulative film in a thickness of 1500 nm is formed. On a diffusion layer 3, a connection hole 5 is opened. Next, a titanium silicide film is formed using a chemical vapor deposition apparatus having a reaction chamber 10, 11, a transporting chamber 12 and a load lock chamber 13, as shown in FIG. 3. One example of the reaction chamber is shown in FIG. 4. In FIG. 4, the reference numeral 14 denotes an upper electrode, 15 denotes a semiconductor substrate, 16 denotes a substrate holder, 17 denotes a resistance heater and 18 denotes an exhaust line.
Namely, as shown in FIG. 1(B), a titanium film 6 in a thickness of 10 nm is formed on an insulative film 4, and a titanium silicide film 7 in a layer thickness of 20 nm is formed on the diffusion layer 3 is formed, by a chemical vapor deposition method employing titanic chloride, hydrogen, argon as a material gas. Furthermore, as shown in FIG. 1(C), in a reaction chamber 11 shown in FIG. 3, a titanium film 6 on the insulative film 1 is nitrided by ammonia for forming a titanium nitride film 8. Then, as shown in FIG. 1(D), a titanium nitride layer 9 in a thickness of 500 nm is formed on the titanium nitride layer 8 and the titanium silicide film 7 using chemical vapor deposition method employing titanic chloride, ammonia, nitrogen as a material gas. Through the process set forth above, the barrier layer is formed in a contact hole.
However, the conventional fabrication process of semiconductor device set forth above encounters the following problems. Since the titanium film is formed in the reaction chamber 10 and nitriding of titanium and deposition of titanium nitride are performed in the reaction chamber 11. Upon formation of the titanium film in the reaction chamber 10, titanium is deposited on portions other than the semiconductor substrate, namely the substrate holder, the upper electrode shown in FIG. 4 and an inner wall of the reaction chamber. The deposited titanium is etched by titanic chloride gas as the material gas to generate TiClx to supply an excessive titanium chloride on the substrate. Therefore, a partial pressure of titanium chloride may be varied depending upon number of substrate to be processed, a desired partial pressure cannot be obtained to vary the titanium film forming speed on the semiconductor substrate. Accordingly, it has been difficult to obtain electric characteristics of the stable contact electrode in the foregoing method.
It is an object of the present invention to provide a fabrication process of a semiconductor device with a titanium film, which can achieve stable titanium film forming speed by avoiding supply of titanium chloride generated by etching of titanium, to a semiconductor substrate and thus by obtaining a desired titanic chloride, and whereby can achieve stable electric characteristics of a contact electrode.
Another object of the present invention is to provide a fabrication process of a semiconductor device with a titanium film, in which a formation step of a titanium nitride film can be performed in a common chamber to formation of the titanium film. A further object of the present invention is to provide a fabrication process of a semiconductor device, which can nitride a residual titanium after removal for further suppress excessive titanium chloride to a substrate by titanium etching, for further stabilizing the titanium film forming speed.
According to the first aspect of the present invention, a fabrication process of a semiconductor device with a titanium film comprises the steps of:
forming a titanium film on a substrate by way of a chemical vapor deposition method; and
removing titanium deposited within a reaction chamber forming the titanium film by a gas containing halogen, following the titanium film forming step.
According to the second aspect of the present invention, a fabrication process of a semiconductor device with a titanium film comprises the steps of:
forming a titanium film on a substrate by way of a chemical vapor deposition method; and
removing titanium deposited within a reaction chamber forming the titanium film and on a semiconductor substrate by a gas containing halogen, following the titanium film forming step.
According to the present invention, since the titanium deposited on the inside of the reaction chamber can be removed, stable titanium forming speed can be obtained. This is because that supply of deposited titanium nitride which is generated by etching of the deposited titanium. Thus, the partial pressure of titanic chloride can be obtained to stabilize electric characteristics of the contact electrode can be achieved.
It should be noted that the wording xe2x80x9cinside of the reaction chamberxe2x80x9d represents a substrate holder, an upper electrode and an inner peripheral wall of the reaction chamber. Also, the gas containing halogen may be selected among chlorine, chloride, fluorine, fluoride, bromine, bromine compound, iodine, iodine compound and the like, for example. A condition, such as process period and so forth upon removal of titanium film by halogen containing gas is not specified. Therefore, the condition may be selected so that titanium deposited on the inside of the reaction chamber may be removed in the extent that the residual titanium on the inside of the reaction chamber may not cause problem in practical use.
In the preferred construction fabrication process of a semiconductor device may further comprise step of forming a titanium nitride film on a semiconductor substrate by way of chemical vapor deposition method within the reaction chamber, after the removing step.
Formation of the titanium nitride film may be performed in the reaction chamber common to formation of the titanium film, or in the alternative, in the reaction chamber different from that used for forming the titanium film. In the conventional process, the titanium deposited in the reaction chamber is etched by the material gas upon formation of the titanium nitride film to generate TiClx or the like to cause peeling off of a Ti film on the substrate. Therefore, in the conventional process, it was essential to use different reaction chambers in formation of the titanium film and the titanium nitride film. In contrast to this, according to the present invention, since titanium deposited in the reaction chamber can be removed by halogen containing gas, TiClx or the like will never be generated during process of formation of the titanium nitride film. Therefore, the single reaction chamber can be used in common for formation of the titanium film and titanium nitride film.
When formation of the titanium film and formation of the titanium nitride film are performed in a common reaction chamber, supply of excessive titanium chloride to the semiconductor substrate can be further suppressed. Namely, after removal of titanium of the inside of the reaction chamber, even if the residual titanium left inside of the reaction chamber, such residual titanium can be nitrided to avoid titanium etching by titanic chloride. Accordingly, the titanium film formation can be further stabilized.
A fabrication process of a semiconductor device may further comprises a step of purging a halogen gas residing in the reaction chamber, after the removing step.
Purging of halogen containing gas can be done by high frequency discharge using argon and hydrogen, for example. Also, diboron, hydrogen phosphide, arsine or the like may be used.
Also, in the preferred construction, the gas containing halogen contains any one of Cl2, HCl, HBr or F2.